Beamforming is an important technology for array systems, the spatial filtering can be achieved by focusing the main beam to the target and null point to the interference. Comparing to the noise suppression method based single-channel, the signal from beamforming output shows lower distortion and higher signal-to-interference plus noise ratio. This study is to investigate the null broadening (bearing, width and depth) control of beamforming, the purpose is to overcome the bearing error between interference and null by producing a broadening null, and to improve the interference signal suppression. Considering the requirements of real-time and broadband in the acoustic system, the fixed beamforming process is chosen and combined with the convex optimization technique. There are several advantages form fixed process that are better robustness due to avoiding the signal self-cancellation from the issue of model mismatch and low-complexity computation contributes to achieving the real-time and broadband spatial filtering in the present process. In the experiment of the chirp signal, the SNR of beamformer output is increased from 2 to 10.5 dB, the correlation coefficient for target is increased from 0.52 to 0.82, and the interference is reduced from 0.54 to 0.07. In the experiment of the broadband voice signal, the SNR of beamformer output is increased from 2 to 6.5 dB, the correlation coefficient for target is increased from 0.37 to 0.68, and the interference is reduced from 0.58 to 0.19. The experimental results verify that the proposed algorithm can effectively controlled the capability of null broadening and have better interference suppression than other algorithms.
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